Gear shift levers of tilt cab vehicles have the characteristic of extending between the cab and the other portion of the vehicle at a position that is displayed from the pivot or hinging point of the cab to the vehicle chassis. The gear shift lever is secured to one or both of the cab and a cooperating gear shifting mechanism. In order to provide quick access to the parts of the vehicle beneath the cab, some provision must be made for the cab to be separated readily from the vehicle without laboriously dismantling the gear shift lever from its adjacent gear shifting mechanism that is outside of the cab and is usually beneath the floor of the cab.
Conventionally, the problem of gear shift lever interference with cab tilting has been overcome by, for instance, the lever being secured to the shifting mechanism so that no portion of the lever travels with the cab when the latter is tilted in which case the floor of the cab may have sufficient articulation to permit the cab to tilt without disconnecting the shifting lever, see U.S. Pat. No. 3,329,229. Alternatively, the shifting lever has been mounted on the floor of the cab with a portion extending therebelow to engage in a quick-releasing manner with a cooperating member of the gear shifting mechanism to permit the shifting lever to move readily upwardly with the cab during tilting, see West German Offenlegungsschrift No. 20 37 310, application date July 28, 1970.
In a commercial embodiment employed in this country, a shift lever is mounted on the floor of a cab to disengage from other parts of the shifting mechanism remaining on the frame when the cab is tilted forward. In this commercial version the shift lever is pinned directly to the cab and includes a bell-shaped portion in the form of a socket extending downwardly beneath the cab floor for engaging a ball member in that portion of the shifter crank mechanism secured to the vehicle beneath the cab floor. In another form of tilt cab-shift lever construction, it has also been proposed to provide an extensible connection between the shifting mechanism beneath the cab and the shifting lever mounted on the cab, so that the connection can extend an appropriate length as the cab tilts upwardly.
Regardless of which type of these construction is provided to permit the cab to tilt without dismantling the gear shift lever, the latter has always been more or less non-resiliently connected to one or both of the cab or the underlying gear shifting mechanism into which the lever extends during operation of the vehicle. Such a connection results in vibrations of the cab, and/or of those other vehicle parts such as the drive mechanism, being transferred to the shifting lever and to the driver as he moves the shifting lever. These vibrations and other cab movements are particularly acute when the rear of the cab is sprung to the vehicle chassis, and the cab is pivoted about its front portion. The resulting wear at the releasable connection can adversely affect shifting to proper gear ratio and may even lead to the vehicle being thrown out of gear during operation.
An example of the kind of problems associated with gear shift levers discussed above is shown in the German Offenlagungschrift No. 20 373 10. As can best be seen in FIGS. 2 and 3, the gear shift lever moves with the cab and is tilted forward as shown in FIG. 1, leaving a funnel or socket portion of the shifting mechanism within the gear transfer mechanism and chassis of the truck. It should be noted that the engagement of the lower finger of the shift lever 5 with an eyelet of the funnel imparts to the shifting shaft the desired movement for shifting of the transmission when the lever is moved by the operator. Although the gear shift lever is releasably connected with the lever socket, the lever is fixedly secured to bearings of a base mounted on the engine floor. As a result, even though shift lever 5 can move with the cab floor during the tilting mode, any vibrations of the cab, as well as those imparted to the lower portion of the shifting lever by other parts of the vehicle during its operation, will be transferred directly to the operator through bearing 4 and the lever. As noted above, this type of structure is quite disadvantageous.
In addition to the problems mentioned above with regard to vibration, the tilt cab constructions of the past have often not provided an acceptable seal between the cab and the portions of the engine and chassis beneath the cab to ensure prevention of leakage of those fumes and other gases which may accumulate beneath the cab. For example, in a chassis-mounted shift control, typically a dynamic-type, separating cab seal is employed which disengages when the cab is raised, such as the seal between a flexible boot which moves with the cab and a shift layer which is mounted to the frame. Because of potentially poor seal to cab alignment and durability, the dynamic seal usually results in a leakage path for under cab air and fumes to be admitted in the cab. An alternative approach, as discussed above, includes the mounting of the shift control rigidly to the cab floor. Although this may provide a positive cab seal it suffers from the vibration problems transferred from the cab to the shift lever as discussed above.